This invention relates to a method of making components for electric motors, in particular a method which utilizes the powder technology to make by a single operation and depending on the type of concerned motor, the body of the stator, or the rotor, which has the permanent magnets embedded therein. Said body may be integral with the casing of a reduction unit or other device to be connected to the motor.
A metal powder with an admixed thermosetting resin is filled in a die in which a punch having the shape of the rotor (in case of d-c motor) has previously been inserted and to which the magnets have been fitted so that these will remain embedded in the stator.
While the specific case of a d-c motor will be referred to in the following description, it is to be understood that the same solution may apply as well to the manufacture of different types of electric motors, such for example, the brushless type.
As is usual for known d-c motors, the stator in these motors generally comprises an external iron sheet frame that, in case of small sized motors, such as those used for small electro-domestic appliances, has frequently been obtained by drawing.
This stator is fitted with permanent magnets that are secured to its frame by means of elastic springs made of steel or the like.
However, this method suffers from some inaccuracy due to various allowances that may add to one another and are related to the magnet thickness, diameter and linearity, the drawing diameter and linearity, for stators made by this process, or the frame winding diameter and related linearity, for stators made by pressing.
In order to avoid any possible interference between the rotor and the magnets when these allowances add to one another, it has been necessary to provide in presently used motors a rather wide gap between said components, which results in a lower motor efficiency that is obtainable when the distance of the magnets from rotor is minimized.
A similar problem arises when making rotors for brushless motors.
On the other hand, production cost is to be controlled and this has kept from having recourse to more elaborate and accurate manufacturing techniques.
In view of the above, it would be desirable that means are provided which enable said gap to be minimized without increasing production cost, thereby to obtain motors of higher power than presently used motors with the size and production costs being the same.